ACE-1 Highlights

The first Aerosol Characterization Experiment (ACE-1) of the International Global Atmospheric Chemistry Project (IGAC) was successfully completed on 15 December 1995. The goal of ACE-1 was to document the chemical, physical, and radiative properties and determine the controlling processes of the aerosol in the remote marine atmosphere. The experiment involved the efforts of over 100 research scientists from 11 countries and included coordinated measurements from the NCAR C-130 aircraft, the NOAA research vessel Discoverer, the Australia fisheries research vessel Southern Surveyor, and land based stations at Cape Grim and Macquarie Island, Australia.

Initial highlights of the experimental results include:

detailed measurements using state of the art instrumentation of the chemical, physical, radiative and cloud nucleating properties of the aerosols in a variety of different environments (background marine atmosphere, volcanic plumes of Kilauea Hawaii and Mt. Ruapehu New Zealand, biomass burning and anthropogenic air masses from Australia). Measurements were made from sea level to 6 km altitude from 75 degrees north to 60 degrees south over the Pacific and Southern Oceans. The over-determined data set will be used in closure studies to test our ability to calculate radiative and cloud nucleating properties of the aerosol from chemical and physical size distributions. The detailed data set will also be used to develop and test aerosol parameterizations in regional and global climate models.

process studies that clearly identified the photochemical formation of new particles in the free troposphere in the vicinity of both low and high level clouds. The new particles were then mixed into the marine boundary layer after cold frontal passages and during periods of synoptic-scale subsidence and convective mixing between the free troposphere and the marine boundary layer. The ultra-fine particles were regularly observed during these meteorological events on Discoverer and at Cape Grim and Macquarie Island. It is clear from these data that particle formation occurs on large spatial and vertical scales and is not confined to regions of precursor gas emissions.

detailed measurements of the biological and chemical characteristics of the water masses south and west of Tasmania and their evolution with time during the course of the experiment. These data will be used to assess both the rate and amount of DMS released from the ocean to the atmosphere and the processes controlling the concentrations of DMS. Initial results suggest biological productivity and DMS production were highest where seasonal thermoclines were being established and where mesoscale mixing of waters of subtropical and subantarctic origin was occurring.

two successful Lagrangian experiments that will be used to quantify the rates and efficiencies of sulfur gas oxidation and the evolution of the aerosol over a 2 day period. Additional shipboard measurements of DMS and SO2 diurnal cycles will be used to constrain oxidation rates and efficiencies.

radiative closure experiments in the volcanic plume of Kilauea and in the background marine atmosphere near Tasmania which will be used to compute clear-sky column-integrated particle scattering. The airborne aerosol lidar was extremely useful in choosing flight altitudes and the lidar data will be used further to scale the in-situ observations over appropriate altitude intervals. The in-situ data will be compared to the simultaneously collected optical depths from the AVHRR satellites and aircraft and ship sunphotometers.

The first ACE-1 data workshop is scheduled for 24-28 June 1996 to review preliminary results from the experiment and to integrate the combined data set. The understanding gained in ACE-1 will be used to study progressively more complex environments. ACE-2 will extend these studies to the North Atlantic Ocean and focus on the anthropogenic aerosols from the European continent and desert dust from the African continent.